Testosterone, 8-Oxo-2′-Deoxyguanosine (8-OHdG) and Cu/Zn Superoxide Dismutase (SOD) in Adult Shuar Males of Amazonian Ecuador: A Test for Evidence of Trade-Offs Between Reproductive Effort and Oxidative Stress

Objectives: Reproductive effort incurs the cost of biological aging and morbidity by compromising somatic maintenance when key resources are limited. Oxidative stress is positively correlated with reproductive effort in adult human females and non-human male animal models, but human males are understudied. We hypothesized that due to its anabolic and metabolic promotion of reproductive effort in human males, testosterone would be positively associated with biomarkers of oxidative stress. Methods: Urinary testosterone in adult Shuar males of Amazonia Ecuador, a foraging/horticultural population, was measured with urinary 8-hydroxy-2′ -deoxyguanosine (8-OHdG), a biomarker of oxidative stress, and Cu/Zn superoxide dismutase (Cu/Zn SOD), a protective antioxidant against oxidative stress. Age and anthropometric measures were included in multivariate models. Results: No significant correlation was observed between testosterone and 8-OHdG, r² = 0.01, p = 0.61, n = 29, or Cu/Zn SOD, r² = 0.0005, p = 0.93, n = 17. Multiple linear regression models including testosterone, Cu/Zn SOD, anthropometrics, and age, with 8-OHdG as the dependent variable, were modestly supportive of an association. The most parsimonious 8-OHdG model included age, Cu/Zn SOD, and testosterone (R^{2 adjusted} = 0.38, p = 0.04, AICc = 141.95). All multivariate models for Cu/Zn SOD were not significant (p > 0.05). Conclusions: Oxidative stress may not be a cost of reproductive effort in this population of adult males; perhaps due to consistently low testosterone levels in non-industrialized populations, differences in the metabolic cost of reproductive effort between males and females (i.e., aerobic metabolism), and/or study limitations based on cross-sectional measures of oxidative stress and testosterone.